New evidence has supported the proposed link between smoking and an increased risk of stillbirth, researchers claim today.
Earlier studies have associated the habit with the chance of babies dying after 24 weeks but before birth as it restricts the growth of the foetus and results in placental complications.
New research published today in BJOG: An International Journal of Obstetrics and Gynaecology claims to have supported this hypothesis, saying the link between smoking and stillbirth risk is significant.
According to the baby charity Tommys, 3,500 babies are stillborn in the UK each year.
Swedish researchers studied stillbirths occurring during the second pregnancy among a total of 526,691 women over an 18-year period from 1983 to 2001.
They recorded smoking habits during the first and second pregnancies and took the maternal age, mother's educational level, cohabitation with the baby's father, mother's country of birth and the interval between first and second pregnancies into account as they are regarded as risk factors in stillbirths.
The researchers concluded that smoking between the first and second pregnancies results in a significant increased risk of stillbirth.
Among heavy smokers who smoked more than ten cigarettes a day during both pregnancies the rate of stillbirth was highest at 4.1 out of every 1,000 women.
Other factors which affect the risk include lower maternal age (under 19 years of age) or higher maternal age (over 35 years old) and long inter-pregnancy periods.
Smokers can lower their risk of having a stillbirth pregnancy however; women who stopped smoking during the early part of their pregnancy lowered the risk of stillbirth as did those who had stopped smoking in the period from the first to the second pregnancy.
Researcher Lovisa Hogberg from the Department of Medical Epidemiology and Biostatistics at the Karolinska Institute in Stockholm said: "This study supports that there is a causal relation between smoking and stillbirth.
"Smoking during pregnancy is a preventable cause of stillbirth, it is therefore important to encourage all pregnant women to quit. Smoking is also known to increase the risk of other adverse pregnancy outcomes."
Commenting on the findings, Professor Philip Steer, BJOG editor-in-chief, said: "We know of the harmful effects of smoking on the foetus because of the direct exposure to toxins when cigarette smoke is inhaled by the mother. The chance of having a tragic stillbirth can therefore be reduced and prevented.
"It is obvious that pregnant women need to stop smoking if they want a healthy baby and it is the duty of doctors and midwives, and more importantly, the mothers themselves, to ensure that they quit."
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